Current production methods involve multiple and costly pressing, sintering, and warm forging operations to form warhead liners from substantially pure or solid solution tungsten or molybdenum powders. This process may take from 12 to 16 weeks to complete a forged and machined liner. Elimination of many of these operations may allow for lower cost and faster response to production orders.
Forging methods include U.S. Pat. No. 4,981,512 entitled METHODS ARE [sic] PRODUCING COMPOSITE MATERIALS OF METAL MATRIX CONTAINING TUNGSTEN GRAIN issued Jan. 1, 1991 to Kapoor. Kapoor discloses a composite material comprising a metal matrix of tungsten grain produced from tungsten powders formed by plasma rapid solidification. The powders are formed into a sintered preform which is consolidated to full density by either hot isostatic pressing, rapid omnidirectional compaction or hot extrusion.
The prior art also includes U.S. Pat. No. 5,000,093 entitled WARHEAD CASING issued Mar. 19, 1991 to Rozner et al. Rozner et al. discloses isostatically pressing a powder mixture to form a preform of an appropriate shape having a density of about 20% to 40% of the theoretical density, and heating the preform in an inert atmosphere at a temperature from 350.degree. C. to 425.degree. C. until the density reaches 60% to 70% of the theoretical density. Rozner et al. does not show a further forging step after the accomplishment of 60% to 70% of the theoretical density through sintering. Rozner et al. also does not show the use of hot isostatic pressing to achieve a greater density.
U.S. Pat. No. 5,119,729 entitled PROCESS FOR PRODUCING A HOLLOW CHARGE WITH A METALLIC LINING issued Jun. 9, 1992 to Nguyen discloses a process for atomizing at least one metal and mixing the resultant metal powder in a broad particle size distribution. The mixture is used to fill in the inner space of a double-walled container of the approximate uniform wall thickness of the lining. This space and the mixture are flushed with hydrogen and sealed in the double walled container in a gas-type manner, and a hot isostatic press is used to form a pressure-molded component. The resulting form of the component may be precise with respect to shape dimensions. The final form of the metallic lining is achieved by machining the pressure molded component.
Such conventional forging methods do not include the use of near net shaping to form warhead liners from substantially pure or solid solution alloys of tungsten or molybdenum. According to current practice, a number of forging steps are believed to be needed to provide for acceptable warhead performance. For the first time, the current invention exploits the fact that hot pressing may yield fine equiaxed grains for uniform properties and consistent performance. It is therefore a motivation of the invention to provide for a process using near net shape blanks and hot pressing to produce warhead liners.
The present invention employs a process of near net shaping of blanks formed from single phase molybdenum and tungsten powders by hot pressing isostatically or dynamically followed by a final forging step after the near net shaping. This process reduces the number of operations needed to complete a liner. Preheating and upset forging steps may be completely eliminated. Forging operations may be eliminated for liner applications where wrought properties are not needed. In addition, the present invention allows control of forging strain distribution in the material.
It is therefore one object of the invention to provide a process for providing near net shape blanks for producing high density refractory metal warhead liners.
It is another object of the invention to reduce the number of steps needed to produce a high density refractory metal warhead liner.
It is yet a further object of the invention to reduce the amount of material necessary to produce high density warhead liners by employing near net shape blanks.
It is yet a further object of the invention to provide for a high density refractory metal warhead liner having wrought properties by using a hot isostatic press with a final forging step on the near net shape blanks.
Other objects, features and advantages of the present invention will become apparent to those skilled in the art through the description of the preferred embodiment, claims and drawings herein wherein like numerals refer to like elements.